The 1946 Law That Put America’s Atomic Bombs Under Civilian Control

The atomic bombings of Hiroshima and Nagasaki hastened the end of World War II but launched a new battle over control of nuclear technology—one that promised extraordinary scientific progress yet threatened civilization itself.

At the dawn of the Atomic Age, the United States faced a momentous question: Who should control the awesome power of the atom? At issue was whether the military should retain responsibility for the nuclear arsenal and research program that it had secretly overseen during wartime. The Atomic Energy Act of 1946, which established the U.S. Atomic Energy Commission, reflected President Harry Truman’s conviction that nuclear weapons and research should ultimately answer to civilian—not military—authority.

As the United States raced Nazi Germany to build the world’s first atomic bomb, the top-secret Manhattan Project operated under military authority with little civilian oversight. U.S. Army General Leslie Groves, placed in charge of the Manhattan Project in 1942, wielded sweeping wartime powers and the greatest operational control over the bomb.

Less than two weeks after becoming president following Franklin D. Roosevelt’s death in April 1945, Truman first learned the full details of the Manhattan Project. A memorandum from Secretary of War Henry Stimson warned that the program would soon produce “the most terrible weapon ever known in human history” and that “modern civilization might be completely destroyed.”

Although Truman knew of plans for an atomic attack on Japan in early August and approved a public statement announcing it, no written record shows him explicitly ordering the bomb’s use. “His actual role in this is extremely peripheral,” says Alex Wellerstein, author of The Most Awful Responsibility: Truman and the Secret Struggle for Control of the Atomic Age. “He never gives any positive order to use the bomb.” Groves, who drafted the formal order authorizing the atomic bombings, later characterized Truman’s role as “one of noninterference.”

The enormous civilian death toll at Hiroshima—which Truman believed would be a “purely military” target—and the subsequent bombing of Nagasaki, which Wellerstein writes “almost certainly surprised” the president, prompted Truman to intervene. At an August 10 Cabinet meeting, he ordered that no additional atomic bombs be used without his express permission. “He said the thought of wiping out another 100,000 people was too horrible,” Secretary of Commerce Henry Wallace recalled. “He didn’t like the idea of killing, as he said, ‘all those kids.’”

“That’s when Truman explicitly puts himself into the chain of command,” Wellerstein says. “Truman realizes after Nagasaki he doesn’t have control—and suddenly desperately wants it.” His order established the requirement for explicit presidential authorization before further atomic attacks, marking a sharp break from his earlier hands-off approach. His response to the destruction caused by the two bombings also helped shape his belief that America’s nuclear program required civilian control.

Because the atomic bomb was unlike any previous military weapon, Truman believed it needed to be controlled differently as well. “The release of atomic energy constitutes a new force too revolutionary to consider in the framework of old ideas,” he said in a special message to Congress on October 3, 1945.

Truman asked Congress to establish the U.S. Atomic Energy Commission (AEC) under civilian—not military—authority. The commission would inherit the Manhattan Project’s vast infrastructure, regulate nuclear technology and assume responsibility for the production and control of fissionable materials and atomic weapons.

The first legislation introduced into Congress fell short of the civilian control many envisioned. Drafted by two War Department lawyers, the May-Johnson Bill called for a nine-member commission that included four representatives from the armed forces and maintained significant military oversight and influence over atomic decisions. In specific situations, even the commission’s administrator could be a military appointee.

Manhattan Project scientists balked. Many viewed the bill as an extension of the wartime program and its culture of secrecy, censorship and strict military control—restrictions they had tolerated only as wartime necessities. They also worried that the government monopoly over nuclear materials and information, backed by penalties of prison time and fines of up to $100,000 for security violations, would stifle scientific innovation.

“The scientists don’t want the Manhattan Project to continue. They don’t think the military ran it well, and most of them loathe General Groves,” Wellerstein says. Scientists also feared that continued military dominance of the atomic program would signal to other nations that the technology was primarily an instrument of war, potentially sparking an international nuclear arms race.

To oppose the legislation, scientists organized through groups including the newly formed Federation of Atomic Scientists. They lobbied Congress and mobilized the American public to support the idea of civilian control, gaining the support of diverse organizations such as the League of Women Voters, the Congress of Industrial Organizations and the American Farm Bureau Federation.

The campaign worked. Truman withdrew his support for the May-Johnson bill, and work began on an alternative.

Momentum built for a Senate bill sponsored by Connecticut Senator Brien McMahon that placed the AEC firmly under civilian leadership. The McMahon bill called for five wholly civilian commissioners appointed by the president to staggered five-year terms and serving at the president’s pleasure. It also eased the previous proposal’s secrecy provisions.

Responding to objections from Groves and others over the exclusion of the armed forces from the commission, lawmakers preserved a military role through an advisory Military Liaison Committee, composed of War Department and Navy representatives. It also provided that the president could “from time to time” order the commission to “deliver weapons to the armed forces for such use as he deems necessary in the interest of national defense.” It created a nine-member committee of civilian scientists to advise the commission on scientific and technical matters, as well as a joint congressional committee to oversee the AEC.

On August 1, 1946, Truman signed the Atomic Energy Act of 1946 into law, committing the country to developing and using atomic energy for “improving the public welfare, increasing the standard of living, strengthening free competition in private enterprise and promoting world peace.” At midnight on December 31, 1946, control over the nation’s atomic energy program passed from the U.S. Army to the civilian Atomic Energy Commission.

As the Cold War intensified, Truman remained committed to civilian authority over America’s nuclear arsenal and resisted mounting pressure during the 1948 Berlin Blockade to transfer atomic bombs to military custody as permitted under the new law.

When Air Force Secretary Stuart Symington argued that the military needed access to the weapons because “our fellas need to get used to handling it,” the president rejected the request. “You have got to understand that this isn’t a military weapon,” Truman said. “It is used to wipe out women and children and unarmed people, and not for military uses. So we have got to treat this differently from rifles and cannon.”

The nuclear arms race complicated Truman’s stance, particularly after the Soviet Union exploded its first atomic bomb in August 1949. The following year, he directed the AEC to pursue development of the hydrogen bomb, a weapon significantly more powerful than the atomic bombs dropped on Japan. In 1951, the Korean War prompted Truman to compromise. He transferred nine nuclear weapons to military custody while retaining civilian authority over their use.

Congress abolished the AEC in 1975, replacing it with the Nuclear Regulatory Commission to oversee the civilian nuclear power industry and the short-lived Energy Research and Development Administration to coordinate weapons development and manage energy research. But the principle established in 1946—that America’s nuclear program would remain under civilian authority—endured.